Elk thistle, Cirsium foliosum(Hook.)
DC. (left). The elk thistle blooms in early summer along
mountain streams and in wet meadows. The young plants are eaten by elk and
bears; the peeled stems are edible for humans. The plants are easily identified
by their size (it is our largest native thistle), by their many prickly
pinnate leaves (foliosum means leafy), and by thebracts
(specialized leaves that cup the flower parts) that extend well above a pinkish
flowerhead that turns brown as the plant matures. Both this plant and
Hookers thistle were gathered by Thomas Drummond (1780-1835), a Scot
who collected plants in western America.

Hookers (or white) thistle,
Cirsium hookerianumNutt. (right).
Hookersthistle, was given the name hookerianum by
Thomas Nuttall in 1841 to honor William Jackson Hooker (1785-1865),
professor of botany at Glasgow and later Director of Englands Royal
Botanic Garden. The plant , a true native, grows at mid- to high
elevations. Its white flowerhead makes identication easy. Cirsium
is a Greek word for a knot of veins, a condition that thistles were used
to treat in the distant past.Hooker's thistle has
a rather localized distribution, for it grows only in Idaho, Washington,
Wyoming, Montana, British Columbia and Alberta.

Jackson Hole thistle, Cirsium
inamoenum(Greene) D. J. Keil
(left). The Jackson Hole thistle (Cirsium
subniveum is an earlier name) grows along roads and trails, blooming
in mid-summer. The plants have a bush-like appearance, growing year after
year in the same location. They have hard, serrated, spiny leaves, and pale
pinkish or lavender, thistle-like flowers, borne on branching stems.

Canadian thistle, Cirsium arvense(L.)
Scop. (right). The misnamed Canadian thistle, like the spotted knapweed,
is a noxious, spreading, exotic plant, originally a native of Eurasia, that
now grows in most states and Canadian provinces. It is a serious, although
not unattractive, weed. It is not easily missed, for it often grows tall,
with deep purple flowers. The plants are deeply rooted, perennial s
that are difficult to eradicate, commonly found growing on disturbed
ground and especially along roads and railroad tracks. We have seen it growing
high in the montane zone, well away from a populated area.

Spotted knapweed, Centaurea
stoebe L. (left). The spotted knapweed (previously
Centaurea maculosa and later Centaurea biebersteinii) is an
import from southwestern Europe that has spread throughout the United States
(including Hawaii), Canada and Mexico. Several species of knapweed grow in
Idaho, but this is the most troublesome. The plants grow high in the montane
zone, turning fields purple by mid-summer. As with many weeds, its flower
is attractive with purple, three-parted rays. The spotted knapweed
can be identified by its straggly, bushy appearance, its purple flowers and
especially by the spotted involucre below the flower parts. Recently it has
been shownas long suspectedthat the roots of knapweed release
a plant poison that aids in its spread. Biologists are studying the possibility
of controlling the plant, with insects imported from its Old World
environment.

Yellow Star-thistle, Centaurea
solstitialisL. (right).
The yellow star thistle is another thoroughly noxious Eurasian
Centaurea that has spread through most of the United States and Canada.
Hardy, deep-rooted, woody. and rapidly spreading, it is found in large
numbers on open mountain slopes at lower elevations, especially in western
Idaho where intensive efforts, both physical (goats eat the plant) and
biological, are being used to control the plant. Its appearance is unique
so that one may identify it at first glance.

Cornflower, Centaurea
cyanus L.(left). The cornflower
(also bachelors button) is, as its appearance suggests, related to
the two centaureas shown above, although a more benign plant. A favorite
ornamental, it has escaped and established itself as a weed throughout North
America. It is a foothill plant in Idaho, turning hillsides blue above Boise.
How serious its weedy proclivities are remains to be seen., The cornflower
is much-loved in Europe, where it is the national flower of Poland.

Common burdock, Arctium minor Bernh.
(right) is a Eurasian import, designated as a noxious weed in several states.
It grows in every state and in all but the northernmost Canadian provinces.
The plants favor disturbed ground and are found in Idaho at least as high
as the montane zone. Despite its weedy status, burdocks are interesting
plants: their dried fruit is beloved by boys, their purple flowers are striking,
all parts of the young plants are edible, and the hooked spines provided
a design for the inventor of Velcro.